Compressed gas, such as air, is often used for starting an aircraft gas turbine, or jet engine. Compressed air flows to a starter which causes rotation of the compressors and the turbines within the jet engine. When sufficient air flows through the jet engine (which may be reflected by turbine speed or otherwise), jet fuel supplied to the engine can be ignited within the combustion area/combustor to start the engine. Without the compressor/turbine rotation provided by the starter, fuel combustion and air flow through the engine may not be sufficient to start the engine.
The flow of compressed air from the air turbine starter may be controlled by a starter valve, such as an air regulating and shut-off butterfly valve. The starter valve, in turn, may be controlled by a control valve. In some embodiments, the control valve is in fluid communication with an air duct within which the starter valve is disposed and receives a portion of air flowing through the duct to move the starter valve to either an open or a close position. Specifically, the portion of air supplied to the control valve causes a pneumatically-operated actuator assembly that is coupled to the starter valve to move the starter valve in either the open or close direction.
Typically, the air duct and actuator in the starter valve are separated from one another by a seal. The seal serves to prevent particles that may be present in the air duct from migrating in to spaces between the starter valve, the central shaft, and/or the actuator assembly. The seal may also prevent particles from becoming trapped within the spaces of the actuator assembly or embedded in the lubricant that lubricates the bearings mounted on the valve shaft.
At times, the air that flows through the starter valve air duct may be hot and pressurized, while the environment within the actuator assembly is not, thus causing a pressure differential between the starter valve duct and actuator assembly, and consequently, across the seal. In these instances, small quantities of the hot, pressurized air may leak across the seal and into the areas previously mentioned. As a result, temperature-sensitive components within the starter valve, such as, for example, elastomeric diaphragms, may be exposed to the hot, pressurized air, which may cause reduced life of the components. Moreover, the hot, pressurized air may be contaminated with particles which can be embedded in the bearing lubricants mentioned above, causing reduced life of the shaft bearings.
Various seal designs have been employed in attempts to address the aforementioned issues. For example, one type of plastic C-seal having grooving thereon has been used, such as the seal illustrated in FIG. 1. This type of seal 10 is typically referred to as a micro-V enhanced C seal. These seals 10 include a plurality of knife cuts 12, wherein material is not removed from the seal 10, to form a ribbed contact 14 on the seal 10. The knife cuts 12 do not have any axial length or depth variations. When the micro-V enhanced C seal 10 is positioned on a shaft, it may not provide an optimal seal with the surface it contacts because the ribbed contact surface 14 may not deflect with changing pressure. Additionally, the ribbed contact surface 14 may not reduce leakage gaps if a flaw is present on the surface with which the seal 10 contacts.
Another type of seal, such as illustrated in FIG. 2 has been employed wherein the plastic C seal 20 has 45-degree wedges 22 machined into or formed thereon to form a ribbed contact surface 24. However, this design also may not provide optimal sealing against the surface with which the seal contacts because the 45-degree wedges 22 may not deflect sufficiently under pressure when they are radially loaded.
Accordingly, there is a need for a seal that is capable of responding to a pressure differential by providing a tighter or lower leakage seal as compared to presently known seals. Additionally, it is desirable to have a seal capable of preventing hot, pressurized and possibly contaminated air from leaking into the aforementioned areas. Moreover, it is desirable that the seal prevent exposure of the temperature-sensitive components to high temperatures and the valve shaft bearings are kept clean. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.